1) Field of the Invention
The field of this invention is the sealing of the bearings especially in high speed peripheral uses where contaminants are present and must be isolated from the bearings.
2) Related Art
Machine tool spindles, because of their high speed rotation, create requirements for maximum reduction or total elimination of contaminants from interacting with the bearings and consequently are a continuing problem for seal and spindle manufacturers. There has long been a belief among seal manufacturers that adding air purging would improve the protection of the bearings, i.e., utilizing a sealing mechanism in conjunction with an air purge. In the prior art lip seals and labyrinth patterns have been combined with an air purge. The air purge pressure has typically been between 5 and 7 psi and has been inserted either outboard or inboard or in the middle of the lip seal labyrinth pattern. These labyrinth patterns with lip seals in combination with seals are and have not been very satisfactory. This is especially true where the seal is subjected to a large amount of coolant deluge and impingement, in which case a substantial amount of coolant can be collected in the area between the labyrinth pattern and the lip seal. The lip seal is then substantially the only sealing member between the bearings and the collected contaminants and coolant. The lip seal, because of pressure and friction, is subjected to a substantial amount of wear and eventual ingress of contaminants or coolant past the lip seal has always occurred.
Speed of rotation or peripheral speed is a factor affecting all sealing devices and lip seals will operate better at low peripheral speeds and for a shorter period of time than other type seals.
Air purge has been operated with bearing isolators similar to those shown and described in U.S. Pat. No. 5,378,000 but with limited success.
Prior air purges have directed the air external to the bearing isolators and the bearing isolator has now merely replaced the lip seal. This arrangement has at least two disadvantages and has not been entirely successful because directing the air purge in front of the bearing isolator causes air, including coolant and debris, due to the pressure, to pass through the isolator and into the bearing housing. Any chips or metallic fines will be trapped by the air pressure around the bearing isolator and will cause increased wear and reduce the bearing efficiency.
Another system of using air to improve theoretically the sealing mechanism of the bearing isolators has been to pressurize the housing. The pressure is normally between 5/10 and 2 psi and is generally introduced at the midpoint of the housing between the bearings. This configuration, when air is applied properly, is compatible with a bearing isolator. However, in as much as the air is being introduced directly into the bearings, cleanliness of the air is extremely important. It is also extremely important to restrict the maximum internal pressure to prevent egress of lubricant and temperature increases in the bearing isolator. This addition of pressure to the bearing housing has been shown to improve bearing isolator performance particularly with slow peripheral or static shafts.
Another example of air combined with bearing isolator usage has been to introduce the air inboard of the bearing isolator and attempting to seal the air from the housing by a normal lip seal or other restricting devices. A port would allow for escape of water or other contaminants contained in the air purge. In this design the lip seal or other restrictive device is still the critical member and limits the life and quality of the sealing effect. This configuration is also mainly satisfactory with slower peripheral speed of spindles or shafts.
Thus, it is important to have a sealing system without utilizing a lip seal and simultaneously able to utilize an air supply which is not necessarily pure, i.e., it may contain contaminants including fluid. Contaminants will migrate past any lip seal, especially at high peripheral speeds.